1. Field of the Invention
The present invention relates to an airbag apparatus that cushions and protects an occupant with an airbag that is inflated by an inflation gas supplied into the airbag, and is suitable for the driver's seat, the passenger seat or the like. The airbag of the airbag apparatus has vent holes allowing the inflation gas therein to be discharged when the internal pressure increases.
2. Description of Related Art
In conventional airbag apparatus, the outer wall of the airbag has a restraining wall that cushions an occupant and a vehicle body side wall that is supported by the vehicle body structure when the occupant is cushioned. The airbag is inflated by an inflation gas supplied into the airbag such that the restraining wall and the vehicle body side wall move away from each other. As described in JP-A-2000-16228, there is an airbag in which vent holes are disposed at a vehicle body side wall and a patch is disposed to cover the outer circumferential side of the vent hole. In the airbag, the remaining inflation gas is discharged from the vent holes to prevent breakage when the internal pressure increases after inflation is finished. The patch has a substantially semicircular outer shape. The patch is disposed such that the straight edge covers the outer circumferential side of the vent hole, toward the center portion of the ring portion of the steering wheel (toward the center portion of the vehicle body side wall). Further, the patch has an arc shape edge connected to the vehicle body side wall of the circumference of the vent hole and a straight edge not connected to the vehicle body side wall. Further, the patch is pressed by the inflation gas to be lifted up from the vehicle body side wall and the inflation gas is discharged from the gap between the straight edge and the vehicle body side wall, when the internal pressure increases.
Further, the patch has a tucked portion that reduces the layer length (area) to ensure airtightness when closing the vent hole. In the airbag, a suture thread sewing the tucked portion is cut when the internal pressure increases. Further, the airbag opens the vent hole by lifting up the patch from the vehicle body side wall (see FIGS. 10 to 13 in JP-A-2000-16228).
However, the airbag in conventional airbag apparatus of three-dimensionally inflates. Accordingly, in the conventional airbag apparatus, a patch having a tucked portion is attached to the circumference of the vent hole in order to ensure airtightness when closing the vent hole. That is, in the airbag apparatus, it is necessary to attach the patch to the circumference of the vent hole of the airbag, for example by sewing. Further, it is necessary to sew in advance the tucked portion to the patch. Therefore, it takes time to dispose the patch in airbag apparatus.
Further, the tucked portion is removed by cutting the suture thread. Therefore, when the suture thread is non-uniformly cut, the exhaust timing from the vent hole of each airbag cannot be stable. That is, it is necessary to make the exhaust timing more stable in the conventional airbag apparatus.